Process for producing sulphuric anhydride and sulphuric acid



Aug. 12, 1924.

M. F. COOLBAUGH ET AL lPROCESS FOR PRODUCING SULPHURIG ANHYDRIDE AND SULPHURIC ACID Filed May 29, 1922 :1n/www4, BBea album",

Patented ug. 12, 1924i.,

' `mrt'. STATESl PTEN MELVILLE F. COOLBAUGH AND` JOHN BURNS RCEAID', OF GO'LDEN, ,COLOR/ADO, .ELS-

SIGNORS TO THE COMPLEX ORES RECOVERIES COMPANY, OF DENVER, COLORADO,

CORPORATION OF COLORADO.

PROCESS FOR PRODUCING SULPHURIC ANHYDRIDE `AND SULPHURIC ACID.

Application led May 29, 1922. Serial No. 564,514.

To all wlw/ml t may concern.'

` Be it known that we, MELVILLE F. Coon- BAUGH and -JOHN BURNS READ, citizens of the United States, and residents of Golden,

6 in the county of Jefferson, State of Colorado,

have invented certain new and useful Improvements in Processes for Producing Sul-l,I

phuric Anhydride and Sulphuric Acid; and

we do declare the following to be a full, 10 clear, and exact description of the invention,

such as will enable others skilledinthe art to which it appertains to make and use the same, reference being had to the accompanying drawings, which form a part of this specilication.

The object of this invention is the produc` tion of sulphuric acid and sulphuric anhydride directly from sulfur bearing minerals by a short cheap method with a high 'pe'rcentage conversion of the sulfur con-` tent of the mineral.

Brieiy the invention comprises a continuous roast of a sulfur bearing mineral containing iron, to -form sulfur dioxide (SO2) and ferrie oxide (Fe203) andto convert the sulfur dioxideA into sulfur trioxide (S03), the ferrie oxide serving as a catalytic agent for SO3 formation. This conversion isfefciently effected by advancing the mineral, air for oxidation and the liberated gases concurrently and continuously in the same direction throughout the process. For the maximum production of sulfur trioxide several conditions should be fulfilled: (l) a temperature should be at- "tained and maintained for the eliicient reaction between sulfur dioxide and oxygen in the presence of ferric oxide; (2') the maximum ferric oxide should be produced; (3)

the ferrie oxide should have the maximum available surface; (4) thetemperature ofthe discharge end of the furnace should be such that only the minimum quantity ofiron sulfates will form.V The sulphuric acid yis produced by thereactionof Wateror water vapor with the sulfur trioxide gas, but this takes place only at a reduced temperature The essential chemical reactions as applied to pyrite are as follows:

More specifically the process, which is illustrated diagrammatically in the accompanying drawings, is as follows: The mineral, such as iron pyrite is suitably crushed to a size of about two mesh and smaller, and is introduced with air into a suitable type of roasting furnace Ywherein the mineral, air for oxidation, liberated gases and steam or water vapor are continuously carried along together, that is"concurrently, throughout the operation.' If the ore or concentrate Acarries a suiiicient amount of moisture no urther addition thereof need be made. Or, steam or water vapor may be added at any place in the furnace, or may even be Vadded to the gases after-they are discharged from the furnace if this is found more convenient or advisable.

The temperature at the charging end of the furnace should be kept below the sinterr ing or clinkering stage or temperature of the mineral, and an amount of air carrying at least an equivalent quantity of oxygen to satisfy the essential chemical reactions should be introduced. v- If the temperature at this point is too highor the mineral is heated up too rapidly, or there is not enough air yor oxygen present, some ferrous silicate or ferrousv oxide (FeO) or magnetite (FesOQ may form. These compounds even in small` quantities associated with ferrie oxide materially retard the conversion of SO2 into 85 SO3d Small quantities of copper,`manga nese and other substances associated with the ferrie oxide materially accelerate this y what slowly and leave an oxide with the maximum numberv of pores which will present the "maximum available surface for gas contact. This maximum surface is very important in determining the rate and extent of the conversion of S02 into S03, since the greater the surface of the catalyzer (Fe205) the higher the rate of conversion.

iEfficient temperatures at the charging end of the furnace have ranges between 250 0'. and 550 0. Above 550 C., the pyrite is liable to sinter, and thereby reduce the yield andalso reduce the eiciency of the ferrie oxid as a catalyst.

The rate of rabbling or stirring themineral in the early stages of roasting has an iny iluence upon the formation of .ferrous silicate, ferrous yoxide and magnetite and also upon the available surface of the ferrie oxide formed. The more rapid the stirring, the

smaller the quantity of the lower oxides of iron, the greater the quantity of Fe203 formed and the greater the available surface of the Fe-203.

The temperature throughout the remainder or the major stage of the desultidizing zone does not require close regulation and may range between 550 C. and 950 C'.

The best temperature conditions for the -convers'ion of S02 into S03 in the'presence of ferrie oxideV will lie also within the above range, that is between v550 C. and 950 C@ AThe exact temperature cannot be stated tures'SO'v tends to break into S 2 and oxygen. This temperaturemust' not be lowered concentration of the S03gas.'

however to a point where appreciable ferricY-oxide and S03 react to form ferric sulfatev or'basic ferrie sulfate. Otherwise, sulfur that is desired in ythe gas willbe retained in the residue. The tempera-ture at which the sulfates form is a function of the The more concentratedthe 'S03 content the higher the temperature required to decompose a given I sulfate or prevent, its formation. The temperature at the discharge end of the furnaceV may therefore vary between rather lwide limits. Temperatures between 450 0.3 and 7 50 0. have given' good results, andvit has been possible to obtain as high as conversion. In Viewo/f .these variations in temperature and other conditions, theconversion zone may loverlap well into the major stageof the desuldizing zone as indicated in the drawings. In fact conversion .may start at the beginning of themajor or with the moisture or water vapor, added or v produced as above described, to form sulpliuric acid which occuis in the form of mist. This acid mistniay be passed through a precipitator or absorbed by any suitable method or recovered in any other manner desired.

40n the other hand it may be desired to use the sulfur trioxide in gaseous form for such purposes as conditioning flue gases to precipitatev the dust `therefrom by electrostatic precipitators. In such an instance the S03 will be removed from the furnace as such and will be introduced into the flue gases in gaseous form either with water vapor under a temperature too high to form acid mist, 'or without water vapor, in

which cases the dust alone will be precipitated and the S03 may be subsequently recovered from the gases passing through the precipitator, in any manner desired such as separate precipitation in the form of acid. However, the sulfur trioxide gas may be yintroduced into the flue gases with water -vapor at a temperature to form acid mist so that the acid will be precipitated with the dust. c

TheV c'alcinedv residue discharged from the furnace may contain values in copper, lead, zinc, gold and silver. If these are sufficiently `high a water or dilute sulphuric acid leach may be applied. The copper and zinc will go into solution and the lead, goldv and silver will remain with the residue.

The values from the solution may be recovered by any of the approved methods. The residue may go to the lead smelter or may be treated with cyanide for the recovery of the gold and silver. lf the residue contains little or no values in lead, gold and silver, and is high of iron content it may go direct to the iron blast furnace.

VIt will be noted that the maximum contact surface per unit of ferrie oxide above mentioned, is presented continuously and is maintained by reason of the continuous, concurrent operation of the process. Thus even if the pores of the oxide become clogged with dust while passing through the furnace and thereby reduce the available contact surface of the oxide, a new supply of fresh material having maximum surface is continuously provided. This overcomes Fany diiiculty experienced by so-called poisoning or exhaustion of the catalytic agent.

We claim: f v y y l. A process for sulphuricacid production comprising roasting an iron-sulfur' mineral at a temperature below the 'sintier-` ing point of the sulphur mineral to prdlce the maximum amount of ferrie oxide and to liberate sulfur dioxide, advancing the roasted materials and liberated gases concurrently with air in contact with one another to form sulfur trioxide, and producing contact of the sulfur trioxide with water vapor under conditions to form`sulphuric acid.

2. A process for producing sulphuric acid comprising roasting a sulfur-iron mineral at a temperature below the sintering point comprising initially roasting a sulfur-iron mineral slowly at a low temperature not above 550 C. for slow liberation of sulfur dioxide, then raising the roasting temperature to complete the roast, advancing the roasted minerals and gases with air to form sulfur tri xide, and causing contact between the trioxi e and moisture under conditionsto form sulphuric acid.

4. A process for producing sulphuric acid comprismg roasting a sulfur-iron mineralv initially at a low temeperature notJ above A 550 C. and stirring the same rapidly during the early stage of the roast, raising the temperature to complete the roast, advanc-` ing the liberated gases and minerals concurrently with air to convert the sulfur dioxideinto sulfur trioxide, and combining the trioxide with moisture to formacid.-

5. A process for the production of sulfur trioxide comprising roasting a sulfur-iron mineral with air at temperatures between 250 C. and 550 C. to form ferric oxide and sulfur dioxide, continuously advancing the roasted minerals and liberated gases with air concurrently, lowering the temperature to form sulfur trioxide, maintaining a temperature high enough for the formation of sulfur trioxide and to prevent its. decomposition and to retard the formation of metal sulfates, and removing the sulfur trioxidef 6. A process for producing sulphuric anhydride comprising roasting a sulfur-iron mineral initially at a low temperature and stirring the same rapidly during the early stages of the-roast, raising the temperature to complete the roast, advancing the minerals and: liberated gases concurrentl in the presence of air at temperatures etween 450 C. and 750 C. to form sulfur trioxide, and to retard the formation of metal sulfates and prevent decomposition of the trioxide.

In testimony whereof we aflix our sig? natures. v

MELVILLE F. COOLBAUGH. JOHN BURNS READ. 

